Okay, so this question is relatively simple. What is the lifespan of the thermal material used underneath the IHS of the i7-4770k (and other 4th gen desktop CPU's)?
I've heard from one place that it has an effective lifespan of around 3 years, but from another that it will last for over 10 years (if not over 15). But I've seen no proof or evidence for either of these statements, so I'd like to try and get a solid answer (maybe with proof?) from someone on here. I usually like people's opinions on such matters (and they shall be very much appreciated); however an actual solid and definite answer would be perfect 
Extra info:
I'm looking to get either an i7-4770k or an i7-4820k (upon its release). I intend to keep the computer for a *long* time, as it will be passed over to a parent when I no longer have a use for it. Obviously the solder will basically last forever (presuming / hoping the 4820k will be soldered), however the 4770k will use less power and is slightly better for general use (slightly higher IPC, and again presuming that the 4820k will be around the same level of performance as the 3770k, going by the performance difference between the 3820 and 2600).